Process for producing aluminum



United States Patent 3,535,108 PROCESS FOR PRODUCING ALUMINUM PaulKobetz and Warren E. Becker, Baton Rouge, La.,

assignors to Ethyl Corporation, New York, N .Y., a corporation ofVirginia No Drawing. Continuation-impart of application Ser. No.

653,622, July 17, 1967. This application Sept. 22, 1969, Ser. No.860,097

Int. Cl. B22f 9/00; C221) 21/00 U.S. Cl. 75-68 20 Claims ABSTRACT OF THEDISCLOSURE Aluminum is formed by exposing alkylaluminum hydride,tertiary amine and a dissociation catalyst (e.g., TiCl to suitabletemperatures for suitable time periods. Instead of forming large amountsof free olefin by-product (as happens in prior art processes) thisprocess coproduces trialkylaluminum:

t-amine & 3R2A1H A1 211ml 3/2 H,

catalyst The process can be conducted at temperatures lower than used inthe prior art processes, or at elevated temperatures. Unitary operationsusing the above reaction for converting crude aluminum into purifiedaluminum are described. One such operation is:

t-aruine Crude Al ZRaAl 3/2 H2 3R2A1H solids t-amine & A1 2R3Al 3/2 Hcatalyst which reduces to:

catalyst Crude Al A1 solids This is a continuation-in-part of our priorcopending application Ser. No. 653,622, filed July 17, 1967 and nowabandoned.

FIELD OF THE INVENTION BACKGROUND Heretofore, considerable attention hasbeen devoted to thermal decomposition processes for producing aluminumfrom alkylaluminum compounds. See, for example, U.S. 2,843,474 grantedJuly 15, 1958; Annalen der Chemie, vol. 629, Nos. l-3, March 1960, pp.210-221; Canadian Pat. 645,138, issued July 17, 1962; British Pat.955,860, published Apr. 22, 1964; U.S. 3,154,407, granted Oct. 27, 1964and U.S. 3,273,996, granted Sept. 20, 1966 (Canadian 682,947, issuedMar. 24, 1964); U.S. 3,170; 787, granted Feb. 23, 1965 (Canadian683,037, issued Mar. 24, 1964); Japanese application 22,474/64apparently published Oct. 10, 1964; U.S. 3,306,732, granted Feb. 28,1967 (Canadian 742,636, issued Sept. 13, 1966); and references citedtherein.

Despite the extent of these prior investigations, several fundamentalshortcomings remain in the art. In the first place, thermaldecomposition of alkylaluminum compounds is a strongly endothermicreaction. Even under the most favorable conditions reported in the abovedisclosures the lowest temperature of decomposition is reported as145-160" C. (U.S. 3,306,732; Table 1).

3,535,108 Patented Oct. 20, 1970 Secondly, in the prior processesinvolving thermal decomposition of ethyl or higher alkylaluminumcompounds, almost quantitative amounts of olefin are produced along withthe aluminum and hydrogen. Although it has been recommended that theolefin and hydrogen be reused to prepare additional alkylaluminumcompound for use in the decomposition step, the reaction of olefin,hydrogen and aluminum is generally not particularly rapid, especiallywhere ethylene is concerned. Moreover, some of the liberated olefintends to be hydrogenated both during the course of the thermaldecomposition step itself (see, for instance, the examples of U.S.3,154,407) and in the reaction of crude aluminum with olefin andhydrogen (see, for instance, U.S. 2,843,474).

Thirdly, unless care is exercised in practicing process technology andinnovations described in connection with some of these prior thermaldecomposition processes, the production of aluminum excessivelycontaminated With aluminum carbide is a likely prospect.

OBJECTIVES Accordingly, an objective of this invention is to provide anovel and useful thermal process for producing aluminum. Another objectis to provide a process of this character which is capable of producingaluminum at temperatures significantly below those heretofore requiredto thermally decompose alkylaluminum compounds. A further object is toprovide a process for producing aluminum which, although utilizingalkylaluminum compounds in its practice, does not result in theliberation or evolution of appreciable quantities of hydrocarbon (e.g.,olefin) byproduct, Whether low or high temperatures are used. Otherimportant objects, features, advantages, and characteristics of thisinvention will become apparent from the ensuing description and appendedclaims.

THE INVENTION In accordance with this invention aluminum is produced bysubjecting a system formed from an alkylaluminum hydride (e.g.,dialkylaluminum hydride), tertiary amine, and a suitable dissociationcatalyst to a temperature sufficiently high and for a period of timesufficiently long to cause formation of aluminum and hydrogen butinsuflicient to cause an appreciable amount of hydrocarbon to beliberated. In this process, the alkylaluminum hydride is converted(probably through one or more transitory intermediates) into aluminum,hydrogen and an alkylaluminum coproduct (trialkylaluminum at least aportion of which is usually complexed with the tertiary amine).

Thus, although the present process has as its principal utility that ofproducing purified aluminum metal, it will be understood and appreciatedthat the process may be considered equally well as a process forconverting alkylaluminum hydride into an alkylaluminum product(principally trialkylaluminum) while at the same time coproducing bothaluminum and hydrogen.

Unlike all of the previously reported processes for producing aluminumfrom alkylaluminum compounds or complexes thereof, an appreciable amountof hydrocarbon (e.g., olefin) is not liberated in the present process.At most, the reaction system or the gas phase associated therewith willcontain perhaps a few Weight percent, based on the weight of aluminumproduced, of free olefin or other free hydrocarbon derived from thealkylaluminum fed into and produced in the process. In other words, theprior processes exemplified by the disclosures cited above areunderstood to proceed via the equations:

On the other hand, the aluminum-forming step of this invention, based onthe available exeprimental evidence, may be depicted (when usingdialkylaluminum hydride) as follows:

tort-amine dz 3R1A1H Al 2R3Al 3/2 112 catalyst Another feature of thisinvention is that it does not require temperatures in the range ofISO-200 C. to 300 C. required in most of the above-cited priorprocesses, nor for that matter temperatures ranging upwards from 145l60C. as described in US. 3,306,732. However, in the present process,temperatures as high as about 260 C. may be utilized in some cases(e.g., when using short residence times) without forming appreciableamounts of free olefin. Moreover, given sufiicient time some of thesystems of this invention will liberate aluminum metal even at roomtemperature.

A further feature of this invention is that the process is capable ofproducing high purity aluminum, e.g., 99.5 weight percent and above.

For practical industrial application, where throughput per unit time isof importance, it is desirable pursuant to this invention to heat asystem formed from the alkylaluminum hydride, tertiary amine and a smallamount of the thermal dissociation catalyst to a temperature within therange of from about 80 C. to about 260 C. with the proviso that with theparticular materials being utilized the temperature is high enough andthe heat is applied long enough to cause formation of aluminum andhydrogen without causing an appreciable amount of hydrocarbon to beliberated.

Generally speaking, the length of time any given system of thisinvention is subjected to the temperature for forming aluminum andhydrogen will be inversely proportional to the temperature being used.For example, periods ranging from many hours to days are used when theprocess is operated at about room temperature up to about 50 C. On theother hand, at temperatures of about 220 C. to about 260 C., theexposure time will be a matter of a few minutes at most.

In most cases the reaction temperatures for most practical operationwill be from about 110 C. to about 220 C. When it is desired to conducta relatively low temperature process within this range (e.g., operatebetween about 110 C. and about 140 C.) the residence time for most ofthe above systems will be from about 5 to about 30 minutes. Whenoperating at the upper end of this temperature range (160-220 C.) theresidence times are usually from about 1 to about minutes. Intermediatetimes are normally employed for the intermediate temperatures of thisrange (140160 C.).

It will be understood and appreciated that the foregoingtemperature-time relationships will vary depending upon the make up ofthe particular reaction system being utilized, and indeed, whateversmall amount of free olefin or other liberated hydrocarbon is deemedacceptable for the purposes at hand. Thus the suitable and the optimumtemperatures and residence or heating times for any given system of thisinvention can readily be determined in each case by a few simpleexperiments. In all cases, however, the temperature and time used willbe sufficient to form aluminum and gaseous hydrogen but insufficient toliberate free hydrocarbon (e.g., free olefin).

When conducting this process it is preferable that the system beingsubjected or heated to the appropriate temperature include atrialkylaluminum, especially one which corresponds to the alkylaluminumhydride being used. This is advantageous because when formingdialkylaluminum hydride, for example, the corresponding trialkylaluminumcompound is almost always present in the product and thus the resultingmixture of alkylaluminum compounds can be utilized in this process. Inshort, it is not necessary to effect a separation between thesealkylaluminum compounds. Further, trialkylaluminum com pounds which haverelatively high thermal decomposition temperatures (e.g.,triethylaluminum) serve as very convenient carriers of thermal energy tothe aluminumforming system. That is to say, separate portions of suchtrialkylaluminum compounds may be preheated to an appropriatetemperature below their thermal decomposition temperature and bedirectly introduced or fed into the thermal decomposition zone wherebythe suitable aluminum-forming temperature is maintained or produced inthe zone at least in part in this manner.

In the preferred operation where the metallic aluminum is produced underthe application of heat energy to the appropriate systems noted above, avariety of heating procedures may be used. For example, heat may beperiodically or continuously supplied so that the appropriatedissociation temperature is continuously maintained within the reactionzone (a procedure useful in continuous operation) or the systems may beformed and then their temperature raised-either in one stage or in aplurality of incremental stages-to the appopirate dissociationtemperature, as in a batch or semi-continuous type operation. Ifdesired, the systems may be formed (except for the catalyst) and quicklybrought up to the appropriate temperature at which point the thermaldissociation catalyst is introduced into the system whereby formation ofmetallic aluminum and evolution of gaseous hydrogen occur. Furthermore,the heat energy may be impressed directly upon the reaction systems(egg. by means of electric heating elements heat transfer from suitableliquids of high thermal capacity and stability or the like) or at leasta portion of the thermal energy may be carried into the thermaldecomposition zone by preheating one or more of the ingredients beingfed into the zone notably the trialkylaluminum feed as explained above.It is also possible to bring the reaction systems in contact withsuitably heated aluminum surfaces (e.g. bars pellets or the like)whereby the aluminum which is produced plates out on or otherwiseadheres to such surfaces. When utilizing the process to prepare aluminumcoatings on other suitable substrates (e.g. metals ceramics etc.) thesubstrates may be preheated to the appropriate temperature and promptlybrought into contact with the reaction system or the substrates may beintroduced into the reaction system and then heated while in contacttherewith by such means as induction heating or the like. These andother suitable methods for the application of heat for effecting theabove process will now be clearly evident to those skilled in the art.

Additional advantageous features characterize this invention. Forexample, the thermal decomposition operations discussed above tend to bequite rapid especially when using an optimum temperature for the systemat hand. This renders the process very useful for industrialapplications insamuch as long thermal decomposition periods can beavoided. Another feature is that the above thermal decompositionoperations do not require the application of reduced pressure, althoughreduced pressures may be used if desired in order to facilitate recoveryof the gaseous hydrogen and excess volatile tertiary amines. In mostcases, however, the aluminum will be produced pursuant to this inventionunder ambient pressure conditions. Though there is no particularadvantage in utilizing elevated pressures, the process is entirelyoperative under such conditions especially where the superatmosphericpressures are not unduly excessive (e.g., are not above about 5000p.s.i.).

To facilitate the recovery of the aluminum produced in accordance withthis invention, it is preferable to conduct a liquid phase thermaldecomposition operation. In this way, the metallic aluminum productappears as a solid phase which can be easily isolated or recovered fromthe liquid reaction system by such means as filtration, centrifugation,and like separation techniques. Thus, in accordance with this preferredliquid phase embodiment, the process comprises forming a liquid phasesystem from alkylaluminum hydride, preferably dialkylaluminum hydride,and tertiary amine and subjecting that system in the presence of a smallamount of the appropriate catalyst to a temperature sufficiently highand for a period of time sufficiently long to cause the formation ofaluminum and hydrogen but insufficient to cause the liberation of anappreciable amount of hydrocarbon (e.g.,. olefin). As noted above, it isdesirable to also include trialkylaluminum in the liquid phase system,especially a trialkylaluminum compound corresponding to thealkylaluminum hydride being utilized. Many trialkylaluminum compoundsassist in maintaining or producing these desirable liquid phase systems.

Any of a variety of alkylaluminum hydrides can be successfully used inthe process. Exemplary materials include dialkylaluminum hydrides suchas dimethylalurninum hydride, dipropyialuminum hydride,diisopropylaluminum hydride, diisobutylaluminum hydride,di-2-methylpentylaluminum hydride, dioctylaluminum hydride,didodecylaluminum hydride, dioctylaluminum hydride, and other similarcompounds. Other closely related alkylaluminum hydrides which may besuccessfully used in this process include alkylaluminum dihydrides(particularly when complexed with tertiary amine which confers stabilityto the molecule) and alkylaluminum sesquihydrides (R Al H Examples ofthese alkylaluminum hydrides are methylaluminum dihydride complexed withtrimethyl amine, ethylaluminum dihydride complexed with triethyl amine,methylaluminum sesquihydride, ethylaluminum sesquihydride, and the like.From the standpoint of availability and ease of synthesis,dialkylaluminum hydrides, especially those in which the alkyl groups arealike and each contains from 2 to about 8 carbon atoms prove to be mostuseful and are preferred. Of these compounds, dihexylaluminum hydride isa typical example. However, of all of the suitable dialkylaluminumhydrides, diethylaluminum hydride is most especially preferred becauseit has a very high aluminum content (second only to dimethylaluminumhydride and methylethylaluminum hydride, both of which are moredifficult and costly to prepare). Moreover, diethylaluminum hydride isan ethylene-based compound (whether made directly from ethylene,aluminum and hydrogen or indirectly from aluminum, hydrogen andtriethylaluminum, the latter being most readily prepared according topresent-day technology from ethylene). It is of course well recognizedthat ethylene is widely available at relatively low cost.

With reference to diethylaluminum hydride as a particularly preferredmaterial for use in the present process, it is worth noting that some ofthe above-cited processes are indicated as being applicable only toalkylaluminum compounds in which the alkyl groups are butyl or higher.Moreover, a cross-reading of Examples 1 and 2 of US. 3,170,787 stronglyindicates that prior thermal decomposition processes are more suitablefor isobutylaluminum compounds than ethylaluminum compounds because thelatter, when utilized in accordance with the prior teachings, tend toform aluminum contaminated with considerable amounts of aluminumcarbide. Selfevidently, this undesirable aluminum carbide impurityresults from homolytic cleavage of carbon-to-aluminum bonds, a type ofcleavage which apparently does not occur when the aluminum is releasedin this process. Thus, pursuant to the present invention, ethylaluminumhydrides and especially diethylaluminum hydride can be utilized withgreat advantage in preparing high purity aluminum.

The trialkylaluminum compounds which are preferably used in conjunctionwith the above-described alkylaluminum hydrides likewise may vary to aconsiderable extent. Thus, efi'ective use may be made of such compoundsas trimethylaluminum, tripropylaluminum, triisobutylaluminum,trihexylaluminum, tridecylaluminum, trioctadecylaluminum, and the like.As noted above, it is generally advantageous, when utilizing acombination of alkylalu minum hydride and trialkylaluminum, that all ofthe alkyl groups be the same and preferably each contain from 2 ing thetrialkylaluminum compound. The same general considerations apply whenusing systems comprising trialkylaluminum and alkylaluminum hydridesother than dialkylaluminum hydride or mixtures of all of these.

The tertiary amines, which are essential for the practice of the presentprocess, are likewise susceptible to considerable variation. Generallyspeaking, members of three typical classes will be found mostsuitablenamely,

(a) amines having the formula R N wherein the R groups are the same ordifferent, and are alkyl, cycloalkyl, aryl, or aralkyl groups;

(b) heterocyclic mononuclear tertiary mono amines; and

(c) amines having the formula /N R R R wherein the R groups can be thesame or different and are alkyl, cycloalkyl, aryl, or aralkyl groups;and R is an alkylene or arylene group and n is an integer from 1 to 6.

Thus, the suitable tertiary amines are typified by such compounds astrimethyl amine, triethyl amine, tributyl amine, N,N-dimethyl aniline,pyridine, and N,N,N,N- tetramethylethylene diamine. Other compounds areexemplified by butyldimethyl amine, trihexyl amine, tridecyl amine,lauryl dimethyl amine, tricyclohexyl amine, tri-(methylcyclohexyl)amines, triphenyl amine, tritolyl amines, trixylyl amines,tri-(p-tertiary butylphenyl) amine, tribenzyl amine,tri-(Z-phenylethyl)amine, ethyldicyclohexyl amine, N,N-diethylaniline,alpha-picoline, beta picoline, gamma-picoline, N-methyl piperidine,N,N,N',N'-tetraethylethylene diamine, N,N,N,N-tetraisopropyl-p-phenylenediamine, and the like. Mixtures of different tertiary amines may beused, if desired. The suitability of any given tertiary amine can easilybe determined by the simple expedient of running a few experiments.

The foregoing tertiary amines tend to form complexes of alkylaluminumcompounds. It will thus be understood and appreciated that the tertiaryamine may be introduced into the heating zone (i.e., thermaldissociation zone) either in whole or in part as a complex with thealkylaluminum hydride or the trialkylaluminum (when utilized), or withboth.

The amount of tertiary amine utilized in this process can vary withinrelatively wide limits. For example, the amine may be present inconsiderable excess relative to the total quantity of alkylaluminumcompound(s) being used. Conversely, the alkylaluminum compound(s) beingutilized can be present in considerable excess relative to the amount oftertiary amine beign used. Generally speaking it is convenient to employmole ratios of alkylaluminum compound(s) :tertiary amine ranging fromabout 20:1 to 1:5. When an excess of tertiary amine (liquid at thereaction temperature) is utilized it serves as a convenient reactiondiluent.

Dissociation catalysts, the use of which is an essential feature of thisinvention, fall in various categories. One general grouping ofcompounds, members of which have been found particularly suitable, maybe represented by the formula MX wherein the X groups can be the same ordifferent and are chlorine, bromine, iodine or alkoxy, and M istitanium, zirconium, hafnium or vanadium. Thus the thermal dissociationcatalysts are typified by titanium tetrachloride, titanium alkoxides(especially those in which the alkoxy groups each contain up to about orcarbon atoms), vanadium tetrachloride, and the like. Similarlyeflicacious catalysts may reside within classes of compounds exemplifierby the tetrahalides of zirconium and hafnium wherein the halogen ischlorine, bromine or iodine; mono-, diand tri-alkoxy metallic halides inwhich the metal is titanium, Zirconium, hafnium or vanadium, and thehalogen is chlorine, bromine or iodine; zinc dihalides such as zincdichloride and zinc dibromide; and the like. It is entirely possiblethat still other suitable catalysts may be found on running appropriatescreening tests. It will thus be appreciated that at present it isdifficult, if not impossible, to exemplify every compound or complexwhich serves to facilitate the conversion of alkylaluminum hydride inthe presence of tertiary amine into aluminum, hydrogen, andalkylaluminum coproduct without liberating appreciable quantities ofhydrocarbons (e.g., free olefin) under the conditions of the process ofthis invention. As noted above, various compounds do function in thismanner and others may be found by screening procedures involvingtechiques such as described in Example X below. Based on availableexperimental results, the most preferred catalysts are titaniumtertachloride and titanium tetraalkoxides in which each alkoxy groupcontains 1 to 16 carbon atoms.

The thermal dissociation catalysts are preferably introduced into thethermal dissociation zone in relatively small quantities-cg, from 1 partper 10,000 parts of aluminum produced up to 1 part per 100 parts ofaluminum produced, these parts being on a weight basis. Preferably, thequantity of catalyst used will be on the low sidei.e., one will normallyuse not much more than the smallest quantity of catalyst which willproduce the desired rate-enhancing result under the particularconditions and with the particular system being used. Whether the abovematerials exhibit their catalytic effects while existing in theiroriginal chemical state or whether they become chemically transformedbefore or during the course of their catalytic activity is not known. Inany event, it has been verified experimentally that the introductioninto the reaction zone of such catalytic materials gives rise to theaccelerated liberaion of aluminum and hydrogen without the formation ofexcessive quantities of free olefin or other free hydrocarbons.

If desired, auxiliary diluents or reaction solvents may be employed inthe present process. For this purpose inert hydrocarbons which areliquid at the reaction temperature (and thus have boiling points inexcess of the reaction temperature) are particularly convenient.Exemplary of the hydrocarbon media which may be employed are theparaffinic, cycloparafiinic, and aromatic hydrocarbon such as petroleumnaphthas, parafiin oils, alkyl benzenes, alkyl naphthalenes, petroleumether, gasoline or kerosene (so long as an appreciable amount ofolefinic unsaturation is not present therein), biphenyl and alkylatedderivatives thereof, and the like. In addition to or in lieu of suchhydorcarbon diluents, use may be made of silicon oils, fluorocarbons orother diluents which do not interfere with the desired reaction or causecontamination of the aluminum produced. In practicing this process theliquid phase may include alkyl alkoxy aluminum compounds such as diethylethoxy aluminum and the like, or ethers such as diethyl ether, dibutylether and diphenyl ether. Generally speaking, it is preferable toconduct the process of this invention in the absence of such auixilarymedia inasmuch as essentially liquid phase systems can readily beproduced by utilizing, in appropriate relative proportions, suitablealkylaluminum component(s) and tertiary amines.

The various materials to be present in the aluminumforming reactionsystem may be fed into the reaction zone in many different ways. Forexample, the alkylaluminum hydride, tertiary amine, dissociationcatalyst, trialkylaluminum (if used) and auxiliary reaction diluent (ifused) may be fed separately or in any appropriate subcombination, eitherconcurrently or in any suitable sequence. When the reaction zone iscontinuously maintained at a highly elevated temperature (e.g., 220260C.) it is desirable to insure that the alkylaluminum component(s) arenot exposed to such temperatures in the absence of the tertiary aminefor any significant period of time inasmuch as such exposure tends tocause homolytic cleavage of the carbon-to-aluminum bonds, liberation offree hydrocarbon (e.g., olefin) and contamination of the metallicaluminum of carboneous impurities (notably aluminum carbide). Thus,where the reaction zone is continuously maintained at these elevatedtemperatures the alkylaluminum hydride and tertiary amine are preferablyconcurrently fed into the zone either as a preformed mixture (in whichat least some alkylaluminumtertiary amine complex will normally exist)or as simultaneously introduced separate feeds. Trialkylaluminum willusually and preferably accompany the alkylaluminum hydride.

In conducting this process one may resort to seeding of finely dividedaluminum powder into the aluminum producing system, if desired. Theseeding of the system with aluminum powder tends to increase the averageparticle size of the aluminum formed via thermal dissociation. In thisconnection, the seed aluminum powder may be added directly to thereactor or it may be first mixed wih alkylaluminum component(s) and theresulting suspension introduced into the reactor. When charging the feeddirectly to the reactor recourse may be had to preheating the powder(e.g., in a suitable oven) to an appropriate elevated temperature sothat the particulate aluminum as fed into the reactor is already at asuitable reaction-promoting temperature.

The aluminum produced in the present process is readily separated fromthe reaction system by various common techniques. For example, when thealuminum is formed in an otherwise essentially liquid phase system, theparticulate aluminum product can be isolated by means of filters,centrifuges or like equipment. It is desirable to wash the isolatedaluminum product with an appropriate inert liquid which will removeresidual quantities of alkylaluminum materials and the like. For thispurpose low boiling paraffinic or aromatic hydrocarbons such as pentane,hexane, heptane, benzene and the like are particularly suitable. Theselow boiling materials are not only inert washing agents but can bereadily removed from the purified aluminum powder by comomn dryingtechniques. In short, suitably volatile inert hydrocarbons will notleave undesirable residues upon the surface of the aluminum product.After the washing operation, the aluminum may be heated to an elevatedtemperature (e.g., 150 C.) under a suitable vacuum (e.g., 10 to mm. Hg)to remove any traces of aluminum alkyl and/or adsorbed hydrogen.

Particularly preferred embodiments of this invention involve the use ofthe above catalytic thermal dissociation operation as a part of acomprehensive process for the chemical refining of crude aluminum. Onesuch embodiment involves at least the following steps:

(1) Converting crude metallic aluminum into a dialkylaluminumhydride-containing liquid phase and a residual solids phase;

(2) Effecting separation between these phases;

(3) Subjecting the separated liquid phase together with tertiary amineand a small amount of the thermal dissociation catalyst to a temperaturesufficiently high and for a period of time sufiiciently long to causethe formation of aluminum and hydrogen but insufficient to cause theliberation of an appreciable amount of hydrocarbon; and

(4) Recovering the aluminum formed in (3).

Various types of crude metallic aluminum are suitable for use inpracticing the above-noted first step of the unitary operation. Thus thecrude aluminum may be in the form of a luminum alloys, aluminum scrap,aluminum dross, reaction products obtained by melting together aluminumoxide-containing material and carbonaceous material (e.g., see US. Pats.2,829,961 and 2,974,032) or the like provided the aluminum-bearingmaterial contains at least some metallic aluminum which is not held inthe tightly bound form of an intermetallic compound. Aluminum-siliconalloys are especially preferred as materials to be refined in thisprocess. Aluminum-silicon alloys can readily be produced at low cost byvarious electrothermic reduction processes (e.g., see British Pat.1,073,025) and thereby serve as an economical source for purifiedaluminum metal. Moreover by using such alloys the residual solids formedin the present process will comprise metallic silicon (usually but notnecessarily associated with other common impurities such as iron,titanium and the like). Such residual solids, which can be readilyrecovered, are of considerable utility in the chemical and allied arts,for example, in steel making processes.

The crude aluminum is preferably employed in subdivided or particulateform although effective use may be made of turnings, chips flakes,ribbons, and the like.

In practicing the above-noted first step there are two general methodsfor converting the crude metallic aluminum into the dialkylaluminumhydride-containing liquid phase. One such method involves reacting thealuminum content with appropriate quantities of an alphaolefin (e.g.,ethylene, propylene, isobutylene, etc.) or internal olefin and hydrogenin the presence of an alkylaluminum catalyst (e.g., triethylaluminum).In this way it is possible to convert this aluminum content into aproduct which in most cases comprises the corresponding dialkylaluminumhydride and trialkylaluminum compounds. As is well known, it isdesirable to suitably activate the aluminum so as to reduce theinduction and re action times. These reactions are generally carried outat somewhat elevated temperatures and pressures. For further detailsrelative to this type of operation, reference may be had, for example,to British Pat. 1,044,735 and US. Pats. 2,787,626; 2,886,581; 2,900,402;3,000,919; 3,016,396; 3,032,574; 3,050,540; 3,050,541; 3,207,773;3,207,774; 3,381,024 and 3,393,217.

The other, and decidedly preferred, method for converting the crudemetallic aluminum into the dialkylaluminum hydride-containing liquidphase involves reacting the crude aluminum with appropriate quantitiesof trialkylaluminum and hydrogen. This reaction proceeds very smoothlyand under proper conditions, quite rapidly, whereby dialkylaluminumhydride can be formed in good yield. Moreover, the use of this type ofprocess makes it possible to recycle or reutilize the trialkylaluminumcoproduct which is formed in the aluminum-producing step.

Therefore, a preferred embodiment of this invention involves convertingthe crude aluminum into an alkylaluminum hydride-containing liquid phaseand residual solids by reacting the aluminum with trialkyl aluminum andhydrogen under apropriate reaction conditions. Such conditionspreferably include use of subdivided crude aluminum alloy, activation ofthe aluminum by common techniques, and utilization of suitable elevatedtemperature and pressure conditions. For further details concerningthese reaction conditions reference may be had, for example, to BritishPat. 1,044,735 and U.S. Pats. 2,885,314; 3,050,540; 3,050,541;3,207,770; 3,207,772; 3,382,269 and 3,393,217.

The above-noted first step may be modified, if desired, so as to produceother suitable alkylaluminum hydridecontaining liquid phases. Thus,although it is preferable that the liquid phase contain a significantproportion of dialkylaluminum hydride, this liquid phase may contain asignificant proportion of dialkylaluminum hydride, this liquid phase maycontain in addition to or in lieu thereof other alkylaluminum hydridessuch as alkylaluminum sesquihydrides. Moreover, the reaction among thecrude aluminum, trialkylaluminum and hydrogen may be effected inadmixture with a tertiary amine, such as those described above. In thiscase, the alkylaluminum hydride product(s) (and the trialkylaluminumalmost always copresent) will tend to exist in the form ofalkylaluminumtertiary amine complexes.

Once the above alkylaluminum hydride-containing iiquid phase and theresidual solids phase have been formed it is a very simple matter toeffect a separation therebetween. Filtration, centrifugation and thelike will most commonly be used. Thereupon the separated liquid phase issubjected to the thermal decomposition process as described above sothat high purity aluminum, hydrogen and trialkylaluminum are formed. Thereaction system will of course also contain the tertiary amine, at leasta portion of which will usually be complexed with the trialkylaluminumcoproduct. Thereupon the aluminum is readily recovered by suchtechniques as filtration or centrifugation.

The separations involved in the above-described unitary process arefacile in that they generally involve separating solids from liquidphases.

An especially advantageous feature of this process is that it issusceptible to re-utilization or recycle of the trialkylaluminumcoproduct, the gaseous hydrogen and the tertiary amine which remainafter separation and recovery of the aluminum product. Naturally it ispossible to reuse less than all of the tertiary amine, trialkylaluminumcoproduct and gaseous hydrogen remaining in or released from thereaction system after removing therefrom the aluminum product. However,a feature of this process is that each of these can be reused in formingadditional alkylaluminum hydride liquid phase for use in the overallprocess. Thus in essence a particularly preferred embodiment of thisinvention involves operation via the following sequence of reactions:

t-arnine Crude Al 2R3A1 3/2 Hz SRZAIH solids t-amine & 3R2A1H Al ZRaAl3/2 H2 Inasmuch as the tertiary amine, the trialkylaluminum coproductand the hydrogen can be reused the foregoing equations reduce to thefollowing:

catalyst Crude Al Purified Al solids It will be seen therefore that thisinvention now makes possible an exceptionally efficient process forproducing aluminum, a process which comprises the following steps:

(1) Forming in a reaction zone a dialkylauminum hydride-containingliquid reaction product from crude metallic aluminum, trialkylaluminum,hydrogen and tertiary amine, said aluminum initially being associatedwith one or more solid impurities;

(2) Effecting separation between the resulting solids and the liquidreaction product;

(3) Heating the liquid reaction product and a small amount of a thermaldissociation catalyst in a heating zone to a temperature high enough andfor a period of time long enough for aluminum and hydrogen to be formedwithout liberating appreciable free hydrocarbon whereby trialkylaluminumand tertiary amine exist in the heating zone;

(4) Recovering aluminum formed in (3); and

(5) Supplying trialkylaluminum, hydrogen and tertiary amine recoveredfrom the heating zone to the reaction zone for producing more of theliquid reaction product by interaction with additional crude metallicaluminum.

Because this process involves use of, in effect, a circulating inventoryof the trialkylaluminum and tertiary amine as well as reutilization ofthe hydrogen instep (1) above, this particularly preferred embodiment iswell suited for operation on a continuous basis. Except for make-upquantities of trialkylaluminum, hydrogen and/or tertiary amine, thisparticular unitary operation in essence uses alkylaluminum compounds ascarriers for conversion of crude aluminum into purified aluminum.

It will be understood and appreciated that although the above unitaryoperations have been described with reference to crude aluminum, theprocess is applicable and extends to the use of commercially-producedaluminum (e.g., aluminum of purities as high as about 99.9 percent) as araw material for conversion into ultra high purity aluminum (e.g., 99.99percent purity or above). Thus the crude aluminum may include suchmaterials as Hallcell aluminum, and the like.

When utilizing aluminum-silicon alloys as a source of aluminum for usein the above comprehensive processes, it is not always necessary(although it is preferable) to introduce a preformed thermaldissociation catalyst into the heating zone in order to produce thepurified aluminum metal. Without desiring to be bound by theoreticalconsiderations, it appears that one or more of the impurity metalsinitially present in the aluminum-silicon alloy (perhaps titanium,vanadium, or the like) tend to form a thermal dissociation catalyst insitu, a small proportion of which appears to be carried into the heatingzone along with the alkylaluminum hydride-containing stream. Thereforeby judicious selection of an appropriate aluminumsilicon alloy in thelight of a few pilot experiments it may be found entirely feasible toconduct the heating operation without introducing into the system one ofthe thermal dissociation catalysts described above. However, for mostpractical operation it is preferable to utilize such thermaldissociation catalysts in any thermal decomposition operation conductedpursuant to this invention inasmuch as these added catalysts insure thatthe aluminum, gaseous hydrogen and trialkylaluminum coproduct will beproduced very rapidly without appreciable liberation of free hydrocarbon(e.g., olefin).

With reference to the above preferred embodiments wherein the crudealuminum is reacted with trialkylaluminum and hydrogen to form thealkylaluminum hydride-containing liquid phase, two additional points areworthy of note. The first is the discovery that the tertiary amine maybe present in this hydroalumination reaction; its presence does notprevent the desired reaction. This makes it possible to reutilize orrecycle all of the efiluent from the heating zone (with the exception ofcourse of the desired aluminum product).

The second point is that residues from the thermal dissociationcatalysts which tend to be carried from the heat ing zone to thehydroalumination reaction zone along with the recycled trialkylaluminumproduct and/ or tertiary amine will not interfere with this particulartype of hydroalumination reaction. Indeed some of these catalystresidues may actually serve as catalysts for the reaction among thecrude aluminum, trialkylaluminum and hydrogen to form the alkylaluminumhydride.

The aluminum when produced in particulate form (i.e., when it is analuminum powder or the like) may, if desired, be converted into variousother forms. For example, the particulate product may be pigged, rolled,or sintered thereby providing other commercially useful forms ofaluminum.

The practice and advantages of this invention will become still furtherapparent from a consideration of the following examples. It is to beunderstood and appreciated, however, that these examples are presentedsolely for the purposes of illustration and are not intended to undulylimit the scope of this invention.

EXAMPLE I A solution containing 25 ml. of tributyl amine, 25 ml. of anequimolar mixture of triethylaluminum and diethylaluminum hydride, andapproximately 0.02 ml. of titanium tetraisopropoxide was heated to 160C. in an oil bath. Gaseous hydrogen was evolved and aluminum metalprecipitated from this mixture. The total reaction period wasapproximately minutes.

EXAMPLE II A run as in Example I was made which difiered only in that0.001 ml. of titanium tetraisopropoxide was used and the solution washeated to 140 C. Approximately 1.1 grams of aluminum precipitated.During the heat up, gaseous hydrogen was evolved.

EXAMPLE III The procedure of Example I was repeated except that 2 ml. ofN,N,N',N-tetramethylethylene diamine was substituted for the tributylamine. At 160 C. this mixture evolved gaseous hydrogen and precipitatedaluminum metal.

EXAMPLE IV A stock solution for use in conducting a series ofexperiments was prepared by mixing together approximately 150 ml. of anessentially equimolar mixture of diethylaluminum hydride andtriethylaluminum and 55 ml. of trimethyl amine. In conducting thisoperation the trimethyl amine had been precooled to a temperature of C.so that its volume could be measured by means of. a calibratedvolumetric flask. In one run a mixture of 25 ml. of this stock solutionand 0.02 ml. of titanium tetraisopropoxide was heated to 160 C. for 5minutes. During this time gaseous hydrogen evolved and aluminum metalprecipitated.

In another run 25 ml. of this stock solution and 0.02 ml. of titaniumtetrachloride were mixed and heated to 160 C. for 5 minutes. During thistime gaseous hydrogen was evolved and metallic aluminum precipitated.

In a third run a mixture of 25 ml. of this stock solution and 0.05 ml.of vanadium tetrachloride was heated to 160 C. for 5 minutes. Duringthis time gaseous hydrogen was liberated and aluminum precipitated.

EXAMPLE V In a series of five runs 20 ml. portions of an essentiallyequimolar mixture of triethylaluminum and diethylaluminum hydride alongwith 0.01 ml. of titanium tetraisopropoxide were added to -milliliterround bottom one-neck flasks. Various quantities of the amines shownbelow were added to the respective flasks:

Run 1.N,N-dimcthyl aniline: 15 ml. Run 2.Tripropyl amine: 20 ml. Run3.Pyridine: 15 ml.

Run 4.Triethyl amine: 10 ml.

Run 5.Triethyl amine: 20 m1.

These five mixtures were then heated in an oil bath to 140 C. In eachcase within 5 minutes complete precipitation of aluminum occurred withgaseous hydrogen being evolved.

EXAMPLE VI An essentially equimolar mixture of diethylaluminum hydrideand triethylaluminum was prepared by hydroalumination of analuminum-silicon-iron-titanium alloy with triethylaluminum and hydrogenat C. and 2000 p.s.i. A solution (40 ml.) containing about 75 Weightpercent of this diethylaluminum hydride-triethylaluminum mixture andabout 25 weight percent of trimethyl amine was heated to 70 C. and atthis temperature 5 ml. of N,N,N,N-tetramethylethylene diamine and 0.0005ml. of titanium tetraisopropoxide were added. Within 3 minutes at 70 C.decomposition had occurred as evidenced by the formation of aluminumpowder and evolution of gaseous hydrogen. In this reaction 1.1 grams ofaluminum, an essentially quantitative yield, was obtained.

In a similar run an additional 40 ml. portion of the above solutioncontaining about 75 weight percent of the above diethylaluminurnhydride-triethylaluminum mixture and about 25 weight percent oftrimethyl amine was heated to 70 C. While at this temperatureapproximately 0.5 ml. of N,N,N,N-tetramethylethylene diamine and 0.0005ml. of titanium tetraisopropoxide were added. Within 10 minutes thedecomposition had occurred (aluminum was formed and hydrogen wasevolved). Once again, an essentially quantitative yield (1.1 grams) ofaluminum was recovered.

EXAMPLE VII A solution was prepared from 25 ml. of a commerciallyavailable, essentially equimolar mixture of diethylaluminum hydride andtriethylaluminum, 25 ml. of tributyl amine and 0.0005 ml. of titaniumtetraisopropoxide. This solution was heated to 120 C. and slowdecomposition to metallic aluminum and gaseous hydrogen occurred. Whilemaintaining the system at 120 C., there was introduced therein 1 gram oftriethylene diamine:

Complete decomposition to aluminum and hydrogen gas occurred immediatelyand from this system an essentially quantitative yield of aluminum wasrecovered. During the course of this decomposition hydrogen wasessentially the only gaseous material liberated.

This procedure was then repeated in the same fashion except that afterreaching the temperature of 120 C. 2 ml. of N,N,N,N-tetramethylethylenediamine was introduced into the solution in lieu of the triethylenediamine. Metallic aluminum was formed and hydrogen was evolved at a fastrate under these conditions.

EXAMPLE VIII To a solution formed from 25 ml. of an essentiallyequimolar mixture of diethylaluminum hydride and triethylaluminum, and0.03 ml. of titanium tetraisopropoxide was added 25 ml. of tributylamine and the resulting system was heated to a temperature in the rangeof 130 144 C. for 40 minutes. During the course of this heating,formation of aluminum and evolution of hydrogen commenced almostimmediately and after the 40 minute period, 1.2 grams of aluminum wererecovered. This corresponded to an essentially quantitative yield.

EXAMPLE IX In one experiment 25 ml. of an essentially equimolar mixtureof diethylaluminum hydride and triethylaluminum was heated to 170 C. for30 minutes. No decomposition reaction occurred.

In another experiment a solution was formed from 25 ml. of anessentially equimolar mixture of diethylaluminum hydride andtriethylaluminum and 25 ml. of tributyl amine. This solution was heatedto 160 C. for 20 minutes. Once again no decomposition occurred.

In a third experiment a solution was formed from 25 ml. of anessentially equimolar mixture of diethylaluminum hydride andtriethylaluminum, 9" ml. of trimethyl amine and 0.05 ml. of titaniumtetraisopropoxide. This solution was heated to 120 C. for minutes duringwhich time hydrogen gas was evolved and aluminum powder precipitated. Atotal of 0.8 gram of aluminum powder was produced in this experiment.

The preceding examples clearly show that various tertiary amines andvarious thermal dissociation catalysts are eifective in the conduct ofthe present process. From Examples VI and VII it is seen that theprocess proceeds efficiently even at low temperatures.

The fact that the present process does not result in a liberation ofappreciable quantity of free hydrocarbon (i.e., olefin) wasexperimentally verified by a series of runs described in Examples Xthrough XII.

EXAMPLE X The apparatus utilized involved a thermal decompositionchamber (a 100-milliliter round bottom one-neck flask) and means forisolating and collecting a representative sample of the gaseous effluentreleased during the course of the thermal decomposition reaction (a gascollecting buret).

In one run 25 ml. of an equimolar mixture of triethylaluminum anddiethylaluminum hydride, 25 ml. of tributyl amine and 0.02 ml. oftitanium tetraisopropoxide were placed in the flask and heated to C. for1 5 minutes, during which time a representative sample of evolved gaswas collected in the gas sampling buret. Analysis of this gaseouseffluent by gas chromatography (VPC) showed 30 p.p.m. of ethylene, thebalance being hydrogen. Inasmuch as 0.8 gram of metallic aluminum wasproduced in this same operation, the 30 p.p.m. of ethylene correspondsto only about 0.004 weight percent of ethylene based on the aluminumproduced. A portion of this aluminum product was analyzed for aluminumcarbide content and was found to contain only 0.006 weight percent ofthis impurity which indicates that the aluminum produced had a purity ofover 99.99 percent.

EXAMPLE XI The procedure of Example X was repeated with the exceptionthat the titanium tetraisopropoxide was introduced into thealkyl-aluminum-tributyl amine system when the latter had been heated upto a temperature of 185 C. Upon introduction of the titaniumtetraisopropoxide, gas evolution and precipitation of aluminum occurredvirtually instantaneously. The gas evolved from the thermaldecomposition itself was found to contain 434 p.p.m. of ethylene, thebalance being gaseous hydrogen. In this run, 0.75 gram of metallicaluminum was produced and thus the foregoing quantity of ethylenecorresponds to about 0.06 percent based on the weight of the aluminumproduct. Analysis of the aluminum product showed it to containapproximately 0.1 percent by weight of aluminum carbide. Consequently inthis experiment aluminum of a purity of about 99.9 percent was achieved.

EXAMPLE XII The procedure of Example X was repeated in the same wayexcept that the titanium tetraisopropoxide catalyst was introduced whenthe reaction mixture had been heated up to 220 C. Once again theevolution of gas and precipitation of aluminum occurred virtuallyinstantaneously. The gas liberated from the thermal decompositionreaction was found to contain 815 p.p.m. of ethylene, the balance beinggaseous hydrogen. In the process of 0.58 gram of aluminum was formed andthus the amount of ethylene liberated during the thermal decompositionreaction corresponded to 0.12 percent based on the weight of aluminumformed. Analysis of the aluminum product for aluminum carbide showedthat it had a purity comparable to that produced in Example XI.

It will be seen from the results of Examples XI and XII that the processof this invention is capable of producing exceedingly pure aluminum evenwhen utilizing relatively high thermal decomposition temperatures. Itwill also be seen that the thermal decomposition time (i.e., residencetime) can be kept quite short especially at the more elevatedtemperatures.

In order to illustrate the preferred unitary (i.e., multistage)operations provided by this invention the following illustrativeexamples are presented.

EXAMPLE XIII In this operation a typical aluminum-silicon alloy was usedto produce a reaction system composed of diethylaluminum hydride andtriethylaluminum hydride and triethylaluminum. In this hydroaluminationreaction tertiary amine was present throughout. More particularly, in a300 milliliter Magne-Stir autoclave were placed ml. of triethylaluminum,10 ml. of N,N,N,N'-tetramethylethylene diamine, 0.2 gram of sodium, and10 grams of powdered alloy (below 325 mesh) containing 68 weight percentaluminum, 27 weight percent silicon, 3 weight percent iron, and 2 weightpercent titanium. The bomb was closed and stirring was started. Thecontents of the bomb were heated to C. under a hydrogen atmosphere at2000 p.s.i. Reaction occurred immediately. After one hour of continuousheating and stirring the autoclave was cooled to room temperature andthe hydrogen gas vented. The contents of the bomb were filtered toremove the residual silicon, iron, titanium and unreacted aluminum. Thissolid residue was washed with benzene and vacuum dried. X-ray analysisof this metallic residue showed 77 percent silicon, 8 percent aluminumand 15 percent others (iron and titanium intermetallics). Thiscorresponds to approximately 95 percent utilization of the free aluminumpresent in the initial alloy.

25 milliliters of the liquid reaction product was added to a100-milliliter round bottom one-flask and immersed in an oil bath at 160C. Upon introduction of 0.02 ml. of titanium tctraisopropoxide,formation of metallic aluminum and evolution of gaseous hydrogencommenced. After approximately minutes the thermal decompositionreaction was essentially complete. The aluminum produced in this secondstage was of high purity and the gaseous efiluent was substantiallyentirely gaseous hydrogen.

EXAMPLE XIV The hydroalumination procedure of Example XIII was repeatedexcept that 0.01 ml. of titanium tetraisopropoxide was added to thehydroalumination reactants. On reaching reaction temperature (110 C.)the reaction commenced immediately and was allowed to proceed for onehour. The residual solids were filtered off, Washed with benzene anddried yielding a total of 4.57 grams. On analysis, this residue wasfound to contain 74 percent silicon, 13 percent aluminum, 13 percentothers, corresponding approximately to a 92 percent utilization of thefree aluminum of the initial alloy.

25 milliliters of the liquid reaction product was heated to 140 C. in anoil bath for a period of approximately 30 minutes. During this timealuminum slowly precipitated and gaseous hydrogen was evolved.

Another 25 ml. portion of this same liquid reaction product wassubjected to the thermal decomposition reaction except that in thisinstance 0.02 ml. of titanium tetraisopropoxide was utilized as thethermal dissociation catalyst. It was found that at 160 C. metallicaluminum and gaseous hydrogen were evolved at a rapid ratethe reactionwas substantially complete within 5 to minutes.

In both cases the metallic aluminum product was of high purity. Likewisein both instances the gaseous effluent from the thermal decompositionreaction was sub stantially entirely gaseous hydrogen.

The thermal decomposition runs of Example XIV illustrate the fact thatunder some conditions it is not necessary to introduce into the thermaldecomposition system a preformed thermal dissociation catalyst. Moreparticularly, it definitely appears that residual quantities of metallicimpurities initially present in the above-described aluminumsiliconalloy formed an active dissociation catalyst in situ. However, acomparison of the respective thermal decomposition results of ExampleXIV serves to show that it is preferable to utilize a preformeddissociation catalyst inasmuch as it significantly accelerates thedesired reaction. A further illustration of this in situ catalystformation is presented in Example XV.

EXAMPLE XV The hydroalumination procedure as described in Example XIIIabove was applied utilizing 14 grams of the above aluminum-siliconalloy, 0.5 gram of sodium, 87 ml. of triethylaluminum, and 15 ml. oftributyl amine. This mixture was heated to 110 C. under an atmosphere of1000 p.s.i. hydrogen for two hours. Thereupon the reaction mixture wascooled to room temperature and the solids filtered off. After separationof these solids approximately 100 ml. of alkylaluminumhydride-containing product remained.

A 25 ml. aliquot of this reaction solution was mixed with 25 ml. oftributyl amine and heated to 140 C. for about 15 minutes. During thistime hydrogen evolved and aluminum metal precipitated. Upon cooling andfiltering, the amount of aluminum metal produced was found to be 0.15gram. A sample of this aluminum was subjected to emission spectrographicanalysis and was found to contain a maximum of 0.1 percent silicon and amaximum of 0.02 percent of iron. Titanium was not detected and theremainder was aluminum. This within the limits of the accuracy of theanalytical procedure used, the aluminum produced in this process wasfound to be at least 99.8 percent pure.

The balance of the above liquid reaction product was allowed to stand atroom temperature for approximately one week at which time it was notedthat metallic aluminum had precipitated. This serves to illustrate thefact that reaction systems of this invention are capable of producingmetallic aluminum even at room temperature if sufficient time isprovided.

As shown by Example XVI below a feature of this invention is that eventhough relatively large quantities of the thermal dissociation catalystsare used, very little of the catalyst residue tends to remain as animpurity in the metallic aluminum produced.

EXAMPLE XVI In a -milliliter round bottom one-neck flask were placed 25ml. of an essentially equimolar mixture of diethylaluminum hydride andtriethylaluminum, 25 ml. of tributyl amine and 0.02 ml. of titaniumtetraisopropoxide. The flask was partially immersed in an oil bathwhereby the reaction mixture was brought to a constant temperature of C.After allowing the reaction to proceed for approximately 5-10 minutes,the flask was withdrawn from the oil bath and the aluminum recovered byfiltration. After washing the aluminum with toluene and drying under aslight vacuum, the aluminum was subjected to emission spectrographicanalysis in order to determine the content of impurities. The analysisshowed that the aluminum contained no more than about 0.02 weightpercent of titanium and other metallic impurities. Thus of the totalavailable titanium present in the reaction mixture, less than about &became associated with the aluminum produced.

When conducting the hydroalumination reaction for converting the crudealuminum into an alkyaluminum hydride-containing product for use in thethermal dissociation reaction, it is desirable though not essential, toemploy a relatively small amount of sodium, sodium hydride or likematerial to enhance the reactivity of the system. Further detailsconcerning such procedures may be found, for example, in US. 3,050,541.

What is claimed is:

1. A process for producing aluminum which comprises subjecting a systemformed from alkylaluminum hydride, tertiary amine, and a dissociationcatalyst to a temperature sufficiently high and for a period of timesufficiently long to cause formation of aluminum and hydrogen butinsuflicient to cause on appreciable amount of hydrocarbon to beliberated.

2. The process of claim 1 wherein said system also includestrialkylaluminum.

3. The process of claim 1 wherein said system is an essentially liquidphase system.

4. The process of claim 1 wherein said system is an essentially liquidphase system, said hydride is a dialkyl aluminum hydride, and saidsystem includes trialkylaluminum corresponding to the dialkylaluminumhydride being utilized.

5. The process of claim 1 wherein said system is an essentially liquidphase system formed from dialkylaluminum hydride and its correspondingtrialkylaluminum in which the alkyl groups each contain from 2 to about8 carbon atoms; a tertiary amine selected from the group consisting oftri lower alkyl amines, N,N-dimethyl aniline, pyridine, andN,N,N,N'-tetramethylethylene diamine; and a dissociation catalystselected from the group 17 consisting of titanium tetrachloride,titanium tetraalkoxides, and vanadium tetrachloride.

6. The process of claim wherein the dialkylaluminum hydride isdiethylaluminum hydride and the trialkylaluminum is triethylaluminum.

7. A process for producing aluminum which comprises heating a systemformed from alkylaluminum hydride, tertiary amine, and a small quantityof a thermal dissociation catalyst to a temperature Within a range offrom about 80 to about 260 C. with the proviso that said temperature ishigh enough and the heat is applied long enough to cause formation ofaluminum and hydrogen without causing an appreciable amount ofhydrocarbon to be liberated.

8. The process of claim 7 wherein said system also includestrialkylaluminum.

9. The process of claim 7 wherein said system is an essentially liquidphase system.

10. The process of claim 7 wherein said system is an essentially liquidphase system, said hydride is a dialkyl aluminum hydride, and saidsystem includes trialkylaluminum corresponding to the dialkylaluminumhydride being utilized.

11. The process of claim 7 wherein said system is an essentially liquidphase system formed from dialkylaluminum hydride and its correspondingtrialkylaluminum in which the alkyl groups each contain from 2 to about8 carbon atoms; a tertiary amine selected from the group consisting oftri lower alkyl amines, N,N-dimethyl aniline, pyridine, andN,N,N',N'-tetrarnethylethylene diamine; and a dissociation catalystselected from the group consisting of titanium tetrachloride, titaniumtetraalkoxides, and vanadium tetrachloride.

12. The process of claim 11 wherein the dialkylaluminum hydride isdiethylaluminum hydride and the trialkylaluminum is triethylaluminum.

13. A process for producing aluminum which comprises:

(a) converting crude metallic aluminum into a dialkylaluminumhydride-containing liquid phase and a residual solids phase;

(b) effecting separation between said phases;

(c) subjecting the separated liquid phase together with tertiary amineand a small amount of a thermal dissociation catalyst to a temperaturesufficiently high and for a period of time sufficiently long to causethe formation of aluminum and hydrogen but insufficient to cause theliberation of an appreciable amount of hydrocarbon; and

(d) recovering aluminum formed in (c).

14. The process of claim 13 wherein said liquid phase includestrialkylaluminum and said crude metallic aluminum is an aluminum alloy.

15. The process of claim 13 wherein said crude metallic aluminum is analuminum-silicon alloy.

16. A process for producing aluminum which comprises:

(a) forming in a reaction zone a dialkylaluminum hydride-containingliquid reaction product from crude metallic aluminum, trialkylaluminum,hydrogen and tertiary amine, said aluminum intially being associatedwith one or more solid impurities;

(b) effecting separation between the resulting solids and the liquidreaction product;

(c) heating the liquid reaction product and a small amount of a thermaldissociation catalyst in a heating zone to a temperature high enough andfor a period of time long enough for aluminum and hydrogen to be formedwithout liberating appreciable free hydrocarbon whereby trialkylaluminumand tertiary amine exist in the heating zone;

((1) recovering aluminum formed in (c); and

(e) supplying trialkylaluminum, hydrogen and tertiary amine recoveredfrom the hetating zone to the reaction zone for producing more of theliquid reaction product by interaction with additional crude metallicaluminum.

17. The process of claim 16 further characterized in that it isconducted on a continuous basis.

18. The process of claim 16 further characterized in that:

(1) it is conducted on a continuous basis;

(2) said crude metallic aluminum is a subdivided aluminum-silicon alloy;

(3) said trialkylaluminum is triethylaluminum;

(4) said temperature is in the range of from about to about C.; and

(5) said temperature is maintained in said range at least in part byfeeding preheated triethylaluminum into the heating zone.

19. The process of claim 16 further characterized in that saidtemperature is from about C. to about 220 C.

20. The process of claim 16 further characterized in that:

(1) said trialkylaluminum is triethylaluminum;

(2) said tertiary amine is selected from the group consisting of:

(a) amines having the formula R N wherein the R groups are the same ordifferent, .and are alkyl, cycloalkyl, aryl, or aralkyl groups;

(b) heterocyclic mononuclear tertiary mono amines; and

(c) amines having the formula N(R-1TI)R R R 11 wherein the R groups canbe the same or different and are alkyl, cycloalkyl, aryl, or araalkylgroups; and R is an alkylene or arylene group and n is an integer from 1to 6; and (3) said catalyst is a compound represented by the formula MX-wherein the X groups can be the same or different and are chlorine,bromine, iodine or alkoxy, and M is titanium, zirconium, hafnium orvanadium.

References Cited UNITED STATES PATENTS 3,268,569 8/1966 Mulder et al260448 3,273,996 9/1966 Ikeda et al 75-.5 3,326,955 6/1967 Brendel eta1. 260 148 L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD,Assistant Examiner U.S. C1. X.R. 260448

